1. Field of the Invention
This invention relates generally to a refrigerating device, and more specifically to a refrigerating device having an inverter circuit for generating alternating voltage and a vibrating compressor driven by the alternating voltage supplied by the inverter circuit wherein the phase of the alternating voltage fed to the compressor is controlled in accordance with ambient temperature of the refrigerating device and/or the evaporator temperature so as to prevent failures such as damage to valve chest due to unwanted compression levels.
2. Description of the Prior Art
In general, a refrigerating device comprises an inverter circuit for generating alternating voltage, a vibrating compressor driven by the alternating voltage supplied by the inverter circuit, a condenser to which the refrigerant compressed by the compressor is supplied, a capillary tube provided on the downstream side of the condenser, an evaporator provided on the downstream side of the capillary tube, etc., and is constructed so that the refrigerant evaporated in the evaporator is returned to the compressor for recompression. In this type of the refrigerating device, however, the piston stroke of the compressor unwantedly increases when the refrigerating device operated at extremely low ambient temperature, causing damage to the valve chest. For instance, when a recreational vehicle (camping car) carrying a refrigerator using this type of refrigerating device is parked on a skiing ground, the refrigerator on board the vehicle is often operated because the temperature within the vehicle is air-conditioned. In such a case, the abovementioned phenomenon often occurs due to low air temperature. This can be explained as follows.
Whereas the refrigerator is operated at room temperature, the condenser connected to the compressor of the refrigerator is exposed to open air temperature, and may be cooled by air temperature as low as -30.degree. C. in extreme cases. As a result, most of the refrigerant is left in liquefied state in the condenser, trickling out little by little to the evaporator. The refrigerant adiabatically expanded there is immediately fed to the condenser by the compressor, bringing the gas pressure in the evaporator and the compressor to a vacuum. This results in an unwanted increase in the piston stroke of the vibrating compressor and eventually in damage to the valve chest.
Needless to say, the vibrating compressor is designed to maintain a resonance between the natural frequency of the mechanical system determined by the elasticity coefficient of refrigerant gas, the spring constant of the resonating spring, etc. and the frequency of the electrical system driving the mechanical system wherever possible. Particularly, a refrigerating device constructed so as to properly maintain a resonance by changing the frequency of the electrical system in accordance with changes in the natural frequency of the mechanical system, as will be described later, tends to suffer directly and sensitively the effect of the abovementioned increase in piston stroke because the electrical system responds with a change in the natural frequency of the mechanical system due to decreased refrigerant gas pressure by changing the frequency of the alternating voltage to maintain the resonance.